Geologic units in Sweetwater county, Wyoming

Additional scientific data in this geographic area

Green River Formation - Laney Member (Eocene) at surface, covers 20 % of this area

Oil shale and marlstone.

Wasatch Formation - Main Body (Paleocene-Eocene) at surface, covers 14 % of this area

Drab sandstone, drab to variegated claystone and siltstone; locally derived conglomerate around basin margins. Lower part is Paleocene.

Bridger Formation (Eocene) at surface, covers 12 % of this area

Greenish-gray, olive-drab, and white tuffaceous sandstone and claystone; lenticular marlstone and conglomerate.

Battle Spring Formation (Paleocene-Eocene) at surface, covers 8 % of this area

Equivalent to, and lithologically similar to locally derived basin-margin conglomerate of Wasatch Formation; merges southward into main body of Wasatch Formation. Lower part is Paleocene.

Dune sand and loess (Pleistocene-Holocene) at surface, covers 6 % of this area

Includes active and dormant sand dunes. In northwestern Wyoming is chiefly loess (age 12,000-19,000 years).

Washakie Formation (Eocene) at surface, covers 5 % of this area

Gray, green, tan, and dull-red tuffaceous arkosic sandstone and claystone.

Alluvium and Colluvium (Pleistocene-Holocene) at surface, covers 4 % of this area

Clay, silt, sand, and gravel in flood plains, fans, terraces, and slopes.

Wasatch Formation - Cathedral Bluffs Tongue (Eocene) at surface, covers 4 % of this area

Variegated claystone and lenticular sandstone; conglomeratic near south margin of Wind River Range.

Fort Union Formation (Paleocene) at surface, covers 4 % of this area

(Northwest, Southwest, and Central Wyoming) - Brown to gray sandstone, gray to black shale, and thin coal beds. (East Wyoming) - Light-colored massive sandstone, drab shale, and thick coal beds.

Playa lake and other lacustrine deposits (Pleistocene-Holocene) at surface, covers 3 % of this area

Chiefly clay, silt, and fine sand. Includes travertine deposits.

Green River Formation - Wilkins Peak Member and Tipton Shale member or Tongue (Eocene) at surface, covers 3 % of this area

Wilkins Peak Member - green, brown, and gray tuffaceous sandstone, shale, and marlstone; contains evaporites in subsurface sections. Tipton Shale Member or Tongue - oil shale and marlstone.

Mesaverde Group - Rock Springs Formation (Upper Cretaceous) at surface, covers 2 % of this area

Rock Springs uplift. White to brown sandstone, shale, and claystone; numerous coal beds.

Green River Formation - Tipton Shale Member or Tongue (Eocene) at surface, covers 2 % of this area

Oil shale and marlstone.

Mesaverde Group - Blair Formation (Upper Cretaceous) at surface, covers 2 % of this area

Rock Springs uplift. Drab-yellow and brown sandstone and sandy shale.

Baxter Shale (Upper Cretaceous) at surface, covers 2 % of this area

Gray to black soft sandy shale and shaly sandstone.

Mesaverde Group - Almond Formation (Upper Cretaceous) at surface, covers 1 % of this area

Rock Springs uplift. White and brown soft sandstone, gray sandy shale, coal, and carbonaceous shale.

Mesaverde Group - Ericson Sandstone (Upper Cretaceous) at surface, covers 1 % of this area

Rock Springs uplift. White massive sandstone; lenticular chert-grit conglomerate in upper part.

Green River Formation - Luman Tongue (Eocene) at surface, covers 1 % of this area

Oil shale, carbonaceous shale, and sandstone.

Wasatch Formation - Niland Tongue (Eocene) at surface, covers 1 % of this area

Brown sandstone, carbonaceous shale, and coal.

Bishop Conglomerate (Oligocene) at surface, covers 1.0 % of this area

Clasts of red quartzite, gray chert, and limestone in a gray to white tuffaceous sandstone matrix.

Green River Formation - Wilkins Peak Member (Eocene) at surface, covers 0.9 % of this area

Green, brown, and gray tuffaceous sandstone, shale, and marlstone; contains evaporites in subsurface sections.

Miocene Rocks (Miocene) at surface, covers 0.8 % of this area

Southwest Wyoming: Southern Rock Springs uplift--Pale-green to tan tuffaceous sandstone and claystone of Miocene(?) age. Conglomerate of uncertain correlation locally at base. Saratoga Valley and west and southwest to Colorado--White massive soft tuffaceous sandstone and lesser amounts of white marl; lower part conglomeratic. Underlies North Park Formation in Saratoga Valley. To the west and southwest is called Browns Park Formation. Rawlins area--White massive soft tuffaceous sandstone; Central Wyoming: White soft tuffaceous sandstone. Locally derived conglomerate in upper and lower parts of sequence; in places lower conglomeratic sequence may be of Oligocene age. In Granite Mountains K/Ar age of tuff in lower part of sandstone sequence about 17 Ma and fission-track age of lower conglomerate about 24 Ma.

Gravel, pediment, and fan deposits (Pleistocene-Holocene) at surface, covers 0.7 % of this area

Mostly locally derived clasts. Includes some glacial deposits along east flank of Wind River Range. Locally includes some Tertiary gravels.

Lance Formation (Upper Cretaceous) at surface, covers 0.5 % of this area

(North Wyoming) - Thick-bedded buff sandstone and drab to green shale; thin conglomerate lenses. (South and Northeast Wyoming) - Brown and gray sandstone and shale; thin coal and carbonaceous shale beds.

Fox Hills Sandstone and Lewis Shale (Upper Cretaceous) at surface, covers 0.5 % of this area

Fox Hills Sandstone (Kfh) - Light-colored sandstone and gray sandy shale containing marine fossils. Lewis Shale (Kle) - Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.

Landslide deposits (Pleistocene-Holocene) at surface, covers 0.1 % of this area

Locally includes intermixed landslide and glacial deposits, talus, and rock-glacier deposits.

Lewis Shale (Upper Cretaceous) at surface, covers 0.1 % of this area

Gray marine shale containing many gray and brown lenticular concretion-rich sandstone beds.

Transitional unit between Battle Spring and Wasatch Formations (Eocene) at surface, covers 0.1 % of this area

Contains interbedded lithologies of Battle Spring (Tbs) and Wasatch (Tw2) Formations.

Alkalic extrusive and intrusive igneous rocks (Quaternary) at surface, covers < 0.1 % of this area

Leucite- and nepheline-rich flows, scoria, and necks.

White River Formation (Oligocene) at surface, covers < 0.1 % of this area

White to pale-pink blocky tuffaceous claystone and lenticular arkosic conglomerate.

Cody Shale (Late Cretaceous) at surface, covers < 0.1 % of this area

(Northern Yellowstone area) - Gray to brown shale and siltstone. (North and South Wyoming) - Dull-gray shale, gray siltstone, and fine-grained gray sandstone.

Undivided surficial deposits (Pleistocene-Holocene) at surface, covers < 0.1 % of this area

Mostly alluvium, colluvium, and glacial and landslide deposits. Primarily in Yellowstone area and Bighorn Mountains.

Terrace gravel (Pliocene-Pleistocene) at surface, covers < 0.1 % of this area

Partly consolidated gravel above and flanking some major streams.

Mesaverde Formation or Mesaverde Group (Upper Cretaceous) at surface, covers < 0.1 % of this area

Mesaverde Formation (north Wyoming) - Light-colored massive to thin-bedded sandstone, gray sandy shale, and coal beds. In Jackson Hole locally contains gold-bearing quartzite conglomerate. North of North Fork Powder River east of the Bighorn Mountains, consists solely of the Parkman Sandstone Member. Mesaverde Group (South Wyoming) - Includes Almond Formation, Ericson Sandstone, Rock Springs and Blair Formations in Rock Springs uplift; Almond Formation (white and brown soft sandstone, gray sandy shale, coal and carbonaceous shale), Pine Ridge Sandstone (light-gray sandstone and thin coal beds), and Allen Ridge (gray sandstone, shale, and thin coal beds) and Haystack Mountains (gray marine sandstone and shale) Formations in Rawlins uplift; Pine Ridge Sandstone (light-gray sandstone and thin coal beds) and Rock River Formation (soft sandstone and sandy shale) in Laramie Basin.

Ice Point Conglomerate (Eocene) at surface, covers < 0.1 % of this area

Reddish-brown conglomerate, chiefly of Paleozoic rock fragments.

Green River Fm--Tipton Tongue (Tertiary) at surface, covers < 0.1 % of this area

Claystone and oil shale; in Sand Wash basin. In extreme northwest includes rocks of Wilkins Peak Member

Green River Fm--Laney Member (Tertiary) at surface, covers < 0.1 % of this area

Claystone, oil shale, and sandstone; in Sand Wash basin

Crooks Gap Conglomerate (Eocene) at surface, covers < 0.1 % of this area

Giant boulders of granite in arkosic sandstone matrix. Reynolds (1976) considers age of eastern exposures to be Oligocene(?).

Wasatch Fm--Cathedral Bluffs Tongue (Tertiary) at surface, covers < 0.1 % of this area

Claystone, mudstone, and sandstone; in Sand Wash basin

Wasatch Fm--Niland Tongue (Tertiary) at surface, covers < 0.1 % of this area

Mudstone, sandstone, and carbonaceous shale; in Sand Wash basin

Wasatch Fm (Tertiary) at surface, covers < 0.1 % of this area

Claystone, shale, and sandstone

Browns Park Fm (Tertiary) at surface, covers < 0.1 % of this area

Sandstone and siltstone; west of Park Range